KR102716826B1 - Using method of the air purifying apparatus using a gas sensing apparatus - Google Patents

Abstract

The air purifier of the embodiment may include a first sensing module that senses at least two gases; and a filtering module including at least two filters that can filter any one of the at least two gases detected by the first sensing module, respectively. Each filter may be provided in response to a harmful gas. The air purifier can actively respond to harmful gases unique to the environment in which it is placed. The harmfulness of the indoor environment caused by harmful gases can be reduced.

Description

{Using method of the air purifying apparatus using a gas sensing apparatus}

The present invention relates to an air purifier using a gas sensing device and a method of using the air purifier.

As the severity of environmental pollution increases, interest in indoor air quality is increasing. Accordingly, the demand for air purifiers that can purify indoor air is increasing among many users. Recently, the demand for air purifiers is increasing due to respiratory infectious diseases such as corona, harmful gases, and diseases transmitted by bad air.

The above air purifier refers to a device that filters out dust, fine dust, bacteria, and chemicals in the air to purify the air. The above air purifier mainly uses a mechanical method based on a hepa filter that performs a dust collection function and an activated carbon filter that performs a deodorization function.

Furthermore, air purifiers that can remove harmful gases such as formaldehyde, VOCs, and the like, along with fine dust, are also introduced. For example, KR101870876B1 discloses an air purifier control method and air purifier that detects various air pollutants such as harmful compounds and fine dust, and adjusts the strength of an ionizer and a fan according to the state of the detected air pollutants.

Meanwhile, a standard technology has been introduced to use a filter that is suitable for an environment containing a certain hazardous gas. Representatively, the registered trademark 3M introduces a filter that responds appropriately to a hazardous gas environment. For example, 'https://www.3m.co.kr/3M/ko_KR/respiratory-protection-kr/products/reusable-respirators' discloses a filter that responds to a specific gas.

Even though the above technology is known, information on how much of which harmful gas is contained in the air, how much of a harmful environment there is, which harmful gas is being removed, and the activity of the filter for which harmful gas are not known.

As another technology, registered patent no. 10074325B1 Indoor gas detection device and indoor air purification system proposes a technology for detecting LPG gas and harmful gases and operating a gas shutoff and air purifier when the concentration exceeds a certain level. This technology only discloses the content of purifying harmful gases, and does not disclose the detection and purification method of each sensor, and the specific operation method.

KR101870876B1 Air purifier control method and air purifier

The present invention aims to provide a gas sensing device capable of confirming the presence or absence of a specific gas and knowing the content of the gas, an air purifier using the gas sensing device, and a method of using the air purifier.

The present invention aims to provide an air purifier having a filter specifically corresponding to a specific gas.

The purpose of the present invention is to provide an air purifier that can identify the replacement cycle of a specific filter that has exhausted its function without replacing a filter that still has its function remaining.

The purpose of the present invention is to provide an air purifier that can actively address the problem of new house syndrome.

The air purifier of the embodiment may include a first sensing module that senses at least two gases; and a filtering module including at least two filters that can filter any one of the at least two gases detected by the first sensing module. Each filter may be provided in response to a harmful gas. The air purifier can actively respond to harmful gases unique to the environment in which it is placed. The harmfulness of the indoor environment caused by harmful gases can be reduced.

Optionally, the at least two gases may include at least two gases having different hazards to the human body. That is, the gases may be distinguished based on their hazards. Accordingly, the hazards may be used as a factor in operating the air purifier.

Optionally, filters that respond to gases that pose a high risk to the human body can be given priority. Accordingly, it is possible to actively respond to biological hazards. For example, it is possible to respond more strictly to highly toxic gases.

Optionally, the at least two filters can predict the replacement time using the detection signal of the first sensing module. Accordingly, the replacement time of the filters can be accurately predicted.

Optionally, a second sensing module may be further included to detect the amount of dust caught in the filter by using the pressure difference before and after the filter. The air purifier can also remove dust. Accordingly, it can respond to various pollutants.

Optionally, a filter may be included that predicts the replacement time using the detection signal of the second sensing module. A filter for filtering dust may be provided individually for convenient use by the user.

A method of using an air purifier according to an embodiment may include: inputting concentration values of at least two gases; and removing a first gas having a high risk to the human body among the at least two gases when the first concentration value of the first gas exceeds a predetermined reference value. Accordingly, a gas having a high risk can be given priority.

Optionally, if the first concentration value does not exceed the reference value, the second gas may be removed when the second concentration value of the second gas having a lower risk to the human body than the first gas exceeds another reference value. The response level may be different depending on the hazard standard. Accordingly, the indoor environment can be managed more safely.

A method of using an air purifier according to an embodiment may include: measuring a concentration of a gas; and, if the change in the concentration of the gas per unit time exceeds a first reference value, determining that the concentration of the gas is increasing, and operating in a first response mode from a third response mode. According to the present embodiment, it is possible to actively respond to sick house syndrome. For example, it is possible to remove harmful gases in advance by considering a situation in which gas emissions occur due to sick house syndrome. For example, it is possible to remove harmful gases in advance in response to daily and/or yearly changes in the aspects of sick house syndrome.

Optionally, after the continuation of the first response mode, if a predetermined condition is satisfied, the second response mode can be operated. Here, the first response mode can have a higher gas filtering ability than the third response mode. Here, the second response mode can have a higher gas filtering ability than the first response mode. Depending on the response mode, operation is possible to quickly purify gas in response to the indoor environment. It is possible to actively respond to gas concentration changes due to new house syndrome.

Optionally, the predetermined condition for driving in the second response mode may include that any time has arrived, or that a predetermined time has elapsed since the first response mode has started. Accordingly, driving may be performed according to the gas removal capability of the current response mode. Accordingly, there is an advantage in that the air purifier can be operated in response to the gas concentration caused by the new house syndrome.

Optionally, the predetermined condition for driving in the second response mode may include that the concentration change per unit time of the gas exceeds the first reference value. According to this condition, it is possible to actively respond to the daily gas concentration change pattern of the new house syndrome. Accurate response operation is possible and malfunction can be prevented. Of course, the gas removal ability can be increased to ensure the safety of the user.

Optionally, when operating in the second response mode, the gas management reference line (l2) can be lowered compared to before. According to the present invention, safety can be maintained by responding to indoor harmful gases that may increase. According to the present invention, a safe indoor environment can be maintained by smoothly responding to specific indoor gas concentration changes due to new house syndrome.

According to the present invention, it is possible to know whether a specific gas exists among a plurality of gases and the concentration value of the specific gas among the plurality of gases.

According to the present invention, the presence or absence of gas and the concentration of gas can be detected by using a small number of gas sensors compared to the number of gases.

According to the present invention, since a single gas is detected using two or more gas sensors, the type of gas and the concentration of the gas can be accurately known.

According to the present invention, a filter can be operated to remove a specific gas.

According to the present invention, filters for specific purposes can be replaced individually without replacing the filter as a whole.

According to the present invention, harmful gases can be actively removed by utilizing the accurately detected concentration of gas.

According to the present invention, users who are sensitive to harmful gases can lead a safer life.

According to the present invention, there is an advantage in that it is possible to respond in advance to the problem of new house syndrome by responding to the emission of harmful gases.

Figure 1 is an exploded view of an air purifier according to an embodiment.
Fig. 2 is a drawing showing the configuration of a filter according to an embodiment.
Fig. 3 is a block diagram of an air purifier according to an embodiment.
Figure 4 is a drawing explaining a method of using a gas sensing device according to an embodiment.
A drawing sequentially showing a method of using a gas sensing device according to the embodiment of FIG. 5.
Figures 6 and 7 are diagrams illustrating mapping of output values to eigenvalue graphs, Figure 6 for the first gas sensor and Figure 7 for the second gas sensor.
Figure 8 is a drawing sequentially showing a method of using a gas sensing device according to an embodiment.
Figure 9 is a flow chart explaining a method of using a gas sensing device according to an embodiment.
Fig. 10 is an exemplary circuit diagram of the above gas sensor.
Figure 11 is a graph showing the change in gas sensor load resistance and the change in output sensor voltage for different gases in an environment with 40 ppm formaldehyde.
Fig. 12 is a drawing explaining a method of using an air purifier according to an embodiment.
Fig. 12 is a drawing explaining a method of using an air purifier according to an embodiment.
Fig. 13 is a drawing graphically explaining a method of using an air purifier according to an embodiment.
Figure 14 is a flow chart explaining a method of using an air purifier according to an embodiment.
Figure 15 is a flow chart explaining a method of using an air purifier according to an embodiment.
Figure 16 is a graph that examines the indoor environments of several childcare facilities over a daily cycle.
Figure 17 is a drawing showing a method of using a conventional air purifier.
Figure 18 is a drawing comparing the usage method of a conventional air purifier and the usage method of the air purifier of the embodiment.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. However, the spirit of the present invention is not limited to the embodiments presented below, and those skilled in the art who understand the spirit of the present invention will be able to easily propose other embodiments included within the scope of the same spirit by adding, changing, deleting, and adding components or limitations on components, but this will also be considered to be included within the scope of the spirit of the present invention.

The present invention may have many embodiments in which its ideas are implemented. In each embodiment, any part may be replaced with a corresponding part or a related part of another embodiment. The present invention may be one of the examples presented below or an example in which two or more are partially combined.

In this description, any part that is lacking in one embodiment may be supplemented by the description of another embodiment. Any part of one embodiment may be expanded or reduced by the description of another embodiment.

In the description of the drawings attached to this description, identical or similar components are given the same reference numbers regardless of the drawing symbols, and redundant descriptions thereof may be omitted.

The suffixes "module" and "part" used for components in this description are given or used interchangeably only for the convenience of writing the specification, and do not have distinct meanings or roles in themselves.

In describing the embodiments disclosed in this application, if it is determined that a detailed description of related known technologies may obscure the gist of the embodiments disclosed in this specification, the detailed description is omitted.

The drawings attached to this description are intended to facilitate understanding of the embodiments disclosed in this specification. It should be understood that the technical ideas disclosed in this specification are not limited by the attached drawings, and that they include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

Terms including ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by the terms. The terms are used only to distinguish one component from another.

When it is said that a component is "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. On the other hand, when it is said that a component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

A singular expression may include a plural expression unless the context clearly indicates otherwise.

In this application, it should be understood that terms such as “comprises” or “has” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

In this application, gas may mean gas. In this application, gas may refer to a state in which a substance is in a gaseous state while changing between liquid/gas/solid states. For example, the gas may mean a harmful gas, but is not limited thereto. In this application, gas may be understood as a concept opposite to general dust/fine dust. In this application, filter may be understood as a concept including a filter that filters out dust.

Figure 1 is an exploded view of an air purifier according to an embodiment.

Referring to FIG. 1, an air purifier (1) can perform the following actions: intake of outside air, filtering out foreign substances from the intaked outside air, and discharging out clean air from which foreign substances have been filtered. In order to perform the above actions, the air purifier (1) can include a motor, a fan assembly (4) that causes airflow by the motor, a filter (2) through which the airflow passes to filter out foreign substances, and a cover (5) that allows replacement of the filter and partitions the inside and outside of the air purifier.

The above air purifier may include at least two air purification modules as a single module in which the fan assembly (4), the filter (2), and the cover (5) are assembled. Accordingly, in order to replace the filter of one air purification module, it is not necessary to stop or replace the other air purification modules. One air purification module may be independent from the other air purification modules. One air purification module and the other air purification modules may filter different gases. The embodiment shows a structure in which the air purification modules are stacked vertically.

A single air cleaning module may include at least two filters (2) for one fan assembly (4). A single air cleaning module may include at least two covers (5) for one fan assembly (4). A single air cleaning module may provide the filters (2) and the covers (5) to correspond to each other. That is, one cover (5) may be opened to replace one filter (2). A single air cleaning module may provide the fan assemblies (4) to correspond to each other for one filter (2). That is, one fan assembly (4) may be operated to operate one filter (2). In the air cleaner of the embodiment, each filter may be operated individually.

The air purifier of the embodiment may include a filter (2) that filters a certain gas and does not filter another gas. The filter may correspond to one gas. The filter may correspond to one gas, and the other may correspond to another gas. The filter may correspond to only one gas. The filter may correspond to only one gas, and the other may correspond to only one gas. The filter may correspond to one gas, and the other may correspond to at least two gases. The filter may correspond to at least two gases. The upper and lower filters may filter different gases.

The air purifier of the embodiment may include at least two gas sensors (6)(7) at a location in contact with the outside air. The greater the number of gas sensors, the more types and numbers of gases can be detected.

The above gas sensors (6)(7) can detect at least two gases. Each gas sensor may detect a gas that is not detected by other gas sensors. For example, there may be a gas that is detected by the first gas sensor (6) and not detected by the second gas sensor (7).

The above gas sensor may detect gases that are not detected by any other gas sensor. In other words, a particular gas may be detected by only one gas sensor. In this case, there may be many types of gases that can be detected. For example, gas 'A' may be detected only by the first gas sensor (6).

Any two gas sensors can detect either gas. For example, both the first and second gas sensors (6)(7) can detect the 'A' gas. There may be a pair of sensors that can detect either gas. For example, in the case where there is a third gas sensor, the third gas sensor may not detect the 'A' gas.

There may be only one pair of sensors capable of detecting both gases.

Figure 2 is a drawing showing the configuration of a filter according to an embodiment.

Referring to Fig. 2, the filter (2) may be provided in a cylindrical shape. The filter (2) may be divided into an arc shape. Fig. 2(a) illustrates that the filter unit is divided into a 180-degree arc shape, Fig. 2(b) illustrates that the filter unit is divided into a 120-degree arc shape, and Fig. 2(c) illustrates that the filter unit is divided into a 90-degree arc shape. A filter unit having a shape other than the arc shape may also be possible. A filter unit having a shape other than the cylindrical shape and a structure other than the cylindrical shape may also be possible.

The above filter unit may be a filter unit that filters different gases. Each of the above filter units may have various purposes, such as semi-HEPA, ULPA, concentrated deodorization, virus removal, formaldehyde removal, VOCc removal, A gas removal, and B gas removal. Each of the above filter units can be replaced independently of each other. Accordingly, there is an advantage of being able to be used economically. The above filter unit may be abbreviated as a filter. This is because when a plurality of filter units exist in a single filter, the filter unit is also a filter.

Fig. 3 is a block diagram of an air purifier according to an embodiment.

Referring to FIG. 3, the air purifier (1) may have a processing module (10) that implements the operation of the air purifier through information processing. The air purifier (1) may have a first sensing module (161) that has at least one gas sensor that detects gas. The air purifier (1) may have a second sensing module (162) that can detect a pressure difference before and after a filter and predict the replacement time of the filter. The air purifier (1) may include a filtering module (15) that has at least one filter.

The first sensing module (161) may include one gas sensor. The first sensing module (161) may include at least two gas sensors. The first sensing module may detect at least two gases. The first sensing module may detect the amount of at least two gases.

The second sensing module (162) can predict the amount of dust, etc. caught in the filter to predict the replacement time of the filter. The second sensing module can utilize the fact that the air pressure before and after the filter changes depending on the amount of dust, etc. The applicant's public disclosure number 10-2021-0004694, 'Air purifier measuring filter life and its control method', provides a more detailed description of the second sensing module (162). To the extent that understanding of the second sensing module is necessary, the description of the present technology is included in this detailed description. The second sensing module (162) can be said to be different from the first sensing module (161) in purpose/composition/function. However, it can be said that the effect is partially the same in that it predicts the replacement time of the filter.

The filtering module (15) may include at least two filters. The at least two filters may filter different substances. The at least two filters may include various filters, such as at least two filters for filtering at least two different gases, a filter for filtering dust, and other filters disclosed in the description of the filter unit. The filtering module (15) may have at least two filters for mainly filtering at least two different gases. The at least two filters may be independently replaceable.

Each filter of the above filtering module (15) may be set with a unique address. Each sensor of the first sensing module (161) may have a unique address. Each sensor of the second sensing module (162) may be set with a unique address. The location of each sensor and each filter may be managed. One sensor and at least one filter may be associated with each other. For example, a gas detected by one sensor may be filtered by at least one filter. As another example, at least one filter that filters a gas detected by one sensor may predict a replacement time based on a signal of one sensor.

The address of each of the above sensors and each filter can be assigned an address by the address assignment unit (13) of the processing module. Each address or the location on the air purifier corresponding to the address can be displayed on the display (17). The user can perform additional work by observing the display information of the display (17). In the case where the address is determined by factory initialization, etc., the address assignment unit can be referred to as an address storage unit. The address assignment unit and the address storage unit can be collectively referred to as an address management unit. For example, blinking of a filter location of a certain address can be promised as an indication of a replacement signal. The associated sensors and filters can be assigned associated addresses by the address assignment unit (13). For example, if the address/location of a sensor detecting 'A' gas is '11-1', the address/location of a filter filtering 'A' gas can be assigned by matching the address as '11-2'. The matched address can be managed adjacently compared to other information. In addition, the location on the air purifier or the location on the display corresponding to each address can also be managed together. The memory (12) can match and store information related to the address and location, the location on the air purifier, and the location on the display.

The above air purifier (1) may further include a power unit (18) that applies power, and a driving unit (19) that performs motor driving/fragrance generation, etc.

The above processing module (10) may include a calculation unit (11). The calculation unit (11) may perform calculation functions such as converting a detection signal of the gas sensor into an amount of gas, selecting a gas using signals of at least two gas sensors, and determining a time for sensor replacement.

The above processing module (10) may include a memory (12). The memory (12) may temporarily or permanently store various information necessary for the operation of the air purifier.

Figure 4 explains a method of using a gas sensing device according to an embodiment.

Referring to Fig. 4, power is supplied to the sensor, and the sensor is exposed to the outside air. The outside air may contain at least one substance. Then, each sensing value of at least two sensors detecting at least two substances is generated and input (S1). For example, a first gas sensor detecting two gases, A and B, and a second gas sensor detecting two gases, A and C, may generate sensing values of different signals, alpha and beta.

Among the above sensing values, at least two sensing values can be mapped to each of the at least two substances (S2). For example, alpha as the sensing value of the first gas sensor and beta as the sensing value of the second gas sensor are mapped to A, B, and C, respectively. The mapping method can be determined in advance by a unique value graph of each sensor. The unique value graph can be a graph that displays predetermined concentration values for different gases according to the sensing voltage sensed by a gas sensor. The unique value graph can be determined in advance for each gas sensor.

If there is a substance whose mapping values of at least two sensing values match within an acceptable range, the mapping value of that substance is output as the concentration value of the detected substance (S3).

Here is an example. As a first example, the value obtained by mapping alpha, which is the sensing value of the first gas sensor, to gas A and the value obtained by mapping beta, which is the sensing value of the second gas sensor, to gas A may coincide within the range of the allowable error. In this case, the sensing value may be output as the concentration value of gas A. However, the value obtained by mapping alpha, which is the sensing value of the first gas sensor, to gas A and the value obtained by mapping beta, which is the sensing value of the second gas sensor, to gas A may be outside the range of the allowable error. In this case, it may be determined that it is not gas A.

As a second example, the outside air may contain only gas B. In this case, the second gas sensor detecting two gases A and C may not react, and only the first gas sensor detecting two gases A and B may react. For example, the second gas sensor may have an output value, and the first gas sensor may have no output value or an output value that is negligible. In this case, the sensing value of the second gas sensor may be output as a concentration value of gas B.

As a third example, the outside air may contain only gas C. In this case, the second gas sensor detecting two gases A and C may react, and the first gas sensor detecting two gases A and B may not react. For example, the first gas sensor may have an output value, and the second gas sensor may have no output value or a negligible output value. In this case, the sensing value of the first gas sensor may be output as a concentration value of gas C.

As a fourth example, if none of the gases A, B, or C are present in the outside air, neither the first nor the second sensor may produce a meaningful output value. In this case, it can be determined that gases A, B, and C were not detected.

As in the example above, by using two sensors that can detect two substances, the existence of three substances and the concentration values of the three substances can be found out. Accordingly, there is an advantage in that the existence of substances and the concentration values of the substances can be found out using a smaller number of sensors than the number of substances to be found out. For example, in order to find out the existence and concentration of three gases, it may be sufficient to use two gas sensors. Accordingly, an economical gas sensing device and a method of using the gas sensing device can be obtained. Of course, the existence of other substances can be found out by additionally using other sensors.

The description of the above method can be more clearly understood with a drawing sequentially showing a method of using a gas sensing device according to the embodiment of FIG. 5.

Referring to FIG. 5, when the gas sensing device is operated, the first gas sensor and the second gas sensor output sensing values as measurement values (S1a) (S1b). The first gas sensor can detect gases A and B. The second gas sensor can detect gases A and C. If the gas measured by each sensor is in the air, the first and second gases can output output values according to the concentration of the gas. In another case, if the gas measured by each sensor is not in the air, the output value of each sensor can be zero or a negligible output value.

The above output values can be mapped to the eigenvalue graphs of each sensor (S2a)(S2b)(S2c)(S2d). The above mapping values can be output as expected concentration values (S3a)(S3b)(S3c)(S3d). Mapping the output values to the eigenvalue graphs will be explained using Figs. 6 and 7 as examples. By mapping the above output values to each gas of the eigenvalue graph, the expected concentration value of the gas can be known.

Here is an example. Assuming that Fig. 6 is a first gas sensor and Fig. 7 is a second gas sensor, the first gas sensor detects hydrogen and toluene, and the second detection sensor detects hydrogen and ammonia. Hydrogen may correspond to gas A in the above example, toluene may correspond to gas B, and ammonia may correspond to gas C.

For example, it is assumed that the first gas sensor shows an output value of 0.3Rs/R0 and the second gas sensor shows an output value of 0.3Rs/R0. The output value of the first gas sensor is mapped to the eigenvalue graphs of hydrogen and toluene, respectively. The mapping value of hydrogen is 40±1ppm with an error of 1. The mapping value of toluene is 2±2ppm with an error of 2. The output value of the second gas sensor is mapped to the eigenvalue graphs of hydrogen and ammonia, respectively. The mapping value of hydrogen is 40±3ppm with an error of 3. The mapping value of ammonia is 80±3ppm with an error of 3.

Using the above mapping values, the gas can be specified (S4a)(S4b)(S4c). Specifying the gas using the mapping values is explained using FIGS. 6 and 7 as examples.

Here is an example. As a first example, among the two mapping values of the first and second gas sensors, it is searched whether there is a mapping value within the error range that matches (S4a). For example, if the gas is hydrogen, the mapping values of the first gas sensor and the second gas sensor are 40±1 ppm with an error of 40±3 ppm. These two values can be said to be mapping values within the error range. Therefore, the current gas can be determined to be hydrogen (S5a). If the mapping values differ significantly, it is out of the error range and therefore cannot be said to be the corresponding gas.

As a second example, if the gas is toluene, the second gas sensor will have no output value. In the first example, the output value of the second gas sensor may be zero. In other words, there may be no response data. Based on the existence of the output value of the first gas sensor, the current gas can be determined to be toluene (S5b).

As a third example, if the gas is ammonia, the first gas sensor may have no output value. In the first example, the output value of the first gas sensor may be zero. In other words, there may be no response data. Based on the existence of the output value of the second gas sensor, the current gas may be determined to be ammonia (S5c).

As a fourth example, the output values of the first and second gas sensors may be zero. In other words, there may be no response data from the first and second gas sensors. Based on the absence of the response data, it can be determined that the three gases are currently absent (S5d).

Likewise, if the concentration of each gas is required, the mapped concentration value can be output. If the above mapped value is not present, no gas can be output.

In the above example, it was explained that the presence or absence and concentration values of three gases can be detected by two sensors capable of detecting two gases. The types of gases that can be detected can increase depending on the types of gases that the sensors can detect and the number of sensors. There can be multiple types of gas sensors that detect at least two gases. Among them, various gas sensing devices can be implemented by using at least two sensors that output reliable mapping values.

Fig. 8 is a drawing sequentially showing a method of using a gas sensing device according to an embodiment. The embodiment of Fig. 8 is different from the embodiment of Fig. 5 in that it uses three gas sensors that detect three gases.

When gas sensing is initiated, the first, second, and third gas sensors output sensing values as measurement values (S31a)(S31b)(S31c). The first gas sensor can detect gases A, B, and C. The second gas sensor can detect gases A, D, and E. The third gas sensor can detect gases B, D, and F. If the gas measured by each sensor is in the air, the first, second, and third gas sensors can output output values according to the concentration of the gas. In another case, if the gas measured by each sensor is not in the air, the output value of each sensor can be zero or a negligible output value.

The above output values can be mapped to the eigenvalue graph of each sensor (S32a to S32i).

The above mapping values can be output as expected concentration values (S33a to S33i).

The gas can be specified using the above mapping values (S34a to S34f). The gas can be specified by using the fact that the mapping values for the same gas from different sensors are within the error range. The gas can be specified based on whether the mapping values are similar.

If the concentration of each gas is required, the mapped concentration values can be output (S35a to S35g).

In this embodiment, it can be confirmed that six gases can be detected by three gas sensors capable of detecting three gases. In order to detect as many gases as possible with as few gas sensors as possible, the following conditions can be satisfied.

First, it is good to have only two sensors that detect one gas together. For example, a sensor that detects gas A only needs two gas sensors, gas sensors 1 and 2.

Second, it is good to have only one sensor that reacts independently for each gas sensor. For example, it is good if gas A reacts only to the first gas sensor. If the above two conditions are satisfied, the largest number of gases can be detected with the smallest number of gas sensors. In addition, some gas sensors can detect only pre-selected gases. It can be said that some gas sensors have no output value or response data for gases other than those pre-selected.

The gas sensing device of the embodiment has the purpose of detecting a large number of gases with a small number of gas sensors. A method of using the gas sensing device according to the embodiment is generally described.

The number of gas sensors that respond to two different gases and the number of gases can satisfy the following rules.

Here, M is the number of different gases that can be detected, and N (two or more) is the number of gas sensors. For example, in the case of a gas sensor that responds to two different gases, if the number of gas sensors is N, it can detect N+1 gases, which is one more than that. M can be at least greater than N.

Explains why.

First, there can be only one pair of gas sensors that react redundantly to one gas. Therefore, each gas can be obtained by combining any one pair of gas sensors. Therefore, it becomes N-1. Second, a gas sensor can independently detect only one or no gases. The cases where there are no independently detectable gases are as follows. Let's say that the first gas sensor detects gases A and B, the second gas sensor detects gases B and C, and the third gas sensor detects gases C and D. In this case, the second gas sensor does not have any independently detectable gases. Applying the circular relationship, the number of independently detectable gases becomes 2. Combining the above two cases, the number of different detectable gases can be N-1+2.

In another case, when combining gas sensors that respond to two different gases and gas sensors that respond to three different gases, the number of gas sensors and the number of gases can satisfy the following rules.

Here, M is the number of different gases that can be detected, N (three or more) is the total number of gas sensors, and L is the number of gas sensors that respond to three different gases. M can be at least as large as N.

Explains why.

First, there can be only one pair of gas sensors that respond to one gas in duplicate. Therefore, each gas can be obtained by combining any one pair of gas sensors. Therefore, it becomes N-1. Second, each gas sensor can independently detect only one or no gas. The following are cases where there is no independently detectable gas.

Let's say that the first gas sensor detects gases A and B, the second gas sensor detects gases B, C, and E, and the third gas sensor detects gases C and D. In this case, the second gas sensor can independently detect gas 'E'. Applying the cyclic relationship, the number of independently detectable gases is the sum of the number that reacts to three different gases and the number that reacts to two different gases at each end, which is 2. Combining the above two cases, the number of detectable different gases can be N-1+L+2.

In other cases, the number of gas sensors responding to three different gases and the number of gases can satisfy the following rules.

Here, M is the number of different gases that can be detected, and N (three or more) is the number of gas sensors. For example, in the case of a gas sensor that responds to three different gases, if the number of gas sensors is N, it can detect 2N gases, which is twice that number. M can be at least as large as N.

Explains why.

First, there can be only one pair of gas sensors that respond to one gas in duplicate. Therefore, each gas can be obtained by combining any one pair of gas sensors. Therefore, it becomes N. Second, there can be only one gas that a gas sensor can detect independently.

For example, suppose that the first gas sensor detects gases A, B, and D, the second gas sensor detects gases B, C, and E, and the third gas sensor detects gases C, D, and F. In this case, the first, second, and third gas sensors can detect gases A, E, and F. Combining the above two cases, the number of different gases that can be detected can be N+N.

In other cases, the number of gas sensors that respond to four different gases and the number of gases can satisfy the following rules.

Here, M is the number of different gases that can be detected, and N (three or more) is the number of gas sensors. For example, in the case of a gas sensor that responds to four different gases, if the number of gas sensors is N, 5/2 gases can be detected. M can be at least greater than N.

Explains why.

First, there can be only one pair of gas sensors that respond to one gas in duplicate. Therefore, each gas can be obtained by combining any one pair of gas sensors. Therefore, it becomes N*3/2. Second, there can be only one (N) gas per gas sensor that can be detected independently.

For example, let's say that the first gas sensor detects gases A, B, C, and D, the second gas sensor detects gases B, E, F, and I, the third gas sensor detects gases C, E, G, and J, and the fourth gas sensor detects gases D, F, G, and H. In this case, gases B, C, D, E, F, and G can be detected by a combination of two gas sensors. In other words, 1.5 times more gases than the number of gas sensors can be detected. The gases that each gas sensor can independently detect are A, I, J, and H. By combining the two cases above, the number of different gases that can be detected can be N*3/2+N.

As seen in the description, as the number of gas sensors in a gas sensing device increases, a greater number of different gases can be detected. As the number of gases that each gas sensor in a gas sensing device can detect increases, a greater number of different gases can be detected with a smaller number of gas sensors.

A set of gas sensors included in a gas sensing device can satisfy the following characteristics.

First, at least two of the above gas sensors may have gases that are not detected by the other gas sensors. That is, one gas may be detected by only one gas sensor.

Second, among at least two of the above gas sensors, any two of the above gas sensors can detect either one gas.

Third, among the at least two gas sensors, there can be only two gas sensors that can detect one gas together. The types of gases to be detected can be further expanded by the third characteristic.

According to the above description, it can be seen that all gases can be detected with a small number of gas sensors compared to the number of detectable gases. Accordingly, if it is confirmed that a certain gas is in the outside air, a filter for filtering the gas can be operated. The cumulative filtering amount of the filter can increase according to the filtering action. By utilizing this, it is possible to find out the replacement time of the filter through which the gas is filtered. At this time, there is an economical advantage because it is independent of other filters that filter other gases or substances. In other words, the cumulative filtering amount of a certain filter can be unrelated to the cumulative filtering amount of another filter.

Figure 9 is a flow chart explaining a method of using a gas sensing device according to an embodiment.

Referring to FIG. 9, a first substance can be detected by the gas sensing device. The substance can be a gas. A filter that filters the first substance can be a part of the entire filter. The part can be independently replaceable. The filtering amount of the first substance can be known by using the concentration of the first substance and the substance absorption rate per unit time filtered by the filter during the operation of the air purifier (S11). That is, the higher the concentration, the higher the substance absorption rate per unit time, and the longer the operating time, the shorter the replacement cycle of the first filter can be.

Afterwards, the current first material filtering amount and the past accumulated filtering amount are added to calculate the current accumulated filtering amount (S12). It is determined whether the current accumulated filtering amount exceeds the critical filtering amount (S13).

If the current accumulated filtering amount exceeds the critical filtering amount, a replacement signal may be generated to replace the first filter that filters the first substance (S15). At this time, the replacement signal may be a replacement signal for only the first filter. If the current accumulated filtering amount does not exceed the critical filtering amount, the past accumulated filtering amount is updated to the current accumulated filtering amount (S14).

The above operation can be performed repeatedly while the air purifier is operating.

The above gas sensor may have different precisions in responding to various gases. As the number of gases detected by a single sensor increases, selection of a more accurate output value may become important. Accordingly, the inventor additionally invented a method for increasing the accuracy of gas mapping by adjusting the load resistance, and a method for accurately sensing the gas concentration value.

Fig. 10 is an exemplary circuit diagram of the gas sensor. Fig. 11 is a graph showing changes in the load resistance of the gas sensor and changes in the output sensor voltage for different gases in an environment with 40 ppm of formaldehyde.

Referring to Fig. 10, the output sensor voltage of the gas sensor is as shown in mathematical expression 5.

V _L is the sensor output voltage, Rs is the sensor resistance (21), and R _L is the load resistance (22). That is, the sensor output voltage pattern can be changed for each gas by adjusting the load resistance.

Referring to Fig. 11, we can see the sensor voltage output for each gas at various load resistances. The things to note are as follows. First, when the load resistance changes at the same sensor voltage, the sensor voltage change amount, that is, the first offset (horizontal offset in Fig. 11), may change for each gas. Second, when the load resistance changes, the sensor voltage change amount, that is, the second offset (vertical offset in Fig. 1) may change for each sensor for the same gas. For example, when the load resistance is 20 kΩ, we can see that the sensor voltage change amount is greater for each gas. For example, when the load resistance is 10 kΩ, we can see that the sensor voltage change amount according to the load is greater for each sensor even for the same gas. Specifically, in the case of the illustrated sensor, when the load resistance is 10 kΩ, the sensor voltage may change more significantly even if the load resistance changes slightly.

By using the above properties, more accurate sensing can be achieved.

First, when the gas sensor outputs the sensing voltage value, the load resistance can be set to the point where the first offset is the largest. For example, in the steps (S1a-S1b) of obtaining output values in FIGS. 5 and 8, the first load resistance can be adjusted to the first offset having the largest first offset to obtain the corresponding output value. In this case, output values that are more distinguishable for each gas can be obtained.

When outputting the concentration value of the gas after the second gas is determined, the sensor having the largest second offset can be used. For example, in the steps (S5a-S3c)(S35a-S35f) of the sensing voltage output of FIGS. 5 and 8, the sensing value of the gas sensor having the largest second offset can be selected to output the corresponding sensing value more accurately. In this case, a more accurate gas concentration value can be obtained.

The above method has the advantage of enabling more accurate operation of the gas sensing device.

The embodiment has the advantage of being able to detect various harmful gases more accurately. A method of using a gas sensing device according to the embodiment utilizing its function is presented.

Fig. 12 is a drawing explaining a method of using an air purifier according to an embodiment. The method of using an air purifier according to an embodiment is characterized by including a new house syndrome mode. The new house syndrome mode can be provided as a setting of the air purifier. When a user sets the new house syndrome mode, automatic operation can be enabled for the safety of the user. The new house syndrome mode can reduce the time that the user is exposed to harmful gases.

Referring to Fig. 12, the method of using the air purifier of the embodiment is explained using the indoor harmful gas line (l1) and the gas management standard line (l2).

The above indoor harmful gas line can show the change in the concentration of harmful gas indoors on a daily basis. The harmful gas of the above indoor harmful gas can be, for example, formaldehyde (HCHO). The above indoor harmful gas line shows that the harmful gas increases in the afternoon on a daily basis. The increase in the harmful gas can increase in two stages. For example, it can increase rapidly and then increase slowly after saturation.

The above gas management reference line (l2) may be a reference line at which the current gas concentration in the air is recognized as harmful. If the harmful gas in the air exceeds the above gas management reference line (l2), the air purifier may operate. Here, the operation of the air purifier may be an operation to remove the harmful gas. Here, the operation of the air purifier may mean that the user does not directly instruct the start of operation at the current time. Here, the operation of the air purifier may include a previously preset new house syndrome mode. Here, the new house syndrome mode may be performed as an automatic operation mode by artificial intelligence, an initial mode of the product, a factory initialization mode, or a user setting mode.

The above gas management reference line (l2) can be temporarily or permanently stored in the memory (12).

For reference, Fig. 16 is a graph that investigates the indoor environment of several childcare facilities on a daily basis. Referring to Fig. 16, it can be seen that the concentration of formaldehyde, etc. increases more than twice in the afternoon on a daily basis. It can be seen that the concentration of the above-mentioned harmful gases increases after the childcare facility is remodeled. As a result of observing the concentration of the above-mentioned harmful gases on an annual basis, it can be confirmed that it continues to leak not only in the year in which the remodeling was performed, but also for several years. The daily change in the concentration of harmful gases in Fig. 16 continues for several years.

According to the above survey results, it can be seen that there is a great need to remove harmful gases in childcare facilities during the afternoon.

Fig. 13 is a drawing illustrating a method of using an air purifier according to an embodiment. Fig. 14 is a flowchart illustrating a method of using an air purifier according to an embodiment. The embodiment may be a drawing showing a method of using an air purifier according to the new house syndrome mode set in the new house syndrome mode.

Referring to FIGS. 13 and 14, the sick house syndrome mode can be performed by any one of various settings (S41). In the sick house syndrome mode, the concentration of gas is measured. The amount of change in the concentration of the measured gas per unit time is determined (S42). For example, the unit time here may be one hour. The harmful gas adjusted to the sick house syndrome mode is represented by the adjusted indoor harmful gas line (l4). The adjusted indoor harmful gas line (l4) gradually increases, and an upward pattern can be detected based on a predetermined first time point (T1).

If the concentration change per unit time exceeds the first reference value, it can be determined that the concentration of the harmful gas significantly increases (S43). In this case, the first response mode can be operated (S44). The first response mode can mean that the ability to filter harmful gases is increased compared to the third response mode. For example, the number of filters that filter harmful gases can be increased, or the wind speed of the air purifier can be increased. If the air purifier includes a ventilation device, the ventilation performance can also be increased.

In the first response mode, the increasing gas concentration can decrease. In the first response mode, the gas management reference line (l2) can be managed as before. In the operating state of the first response mode, the gas concentration may not exceed the gas management reference line. In the first response mode, the ability of the air purifier to remove harmful gases can be preset to maintain the gas management reference line. The regulated indoor harmful gas line (l4) can increase by a predetermined amount even after the first response mode. The concentration of the gas can decrease as the first response mode continues.

If the concentration change per unit time does not exceed the first reference value, it can be determined that the concentration of the harmful gas is significantly increasing (S43). In this case, operation can continue in the third response mode (S45). The third response mode may mean the default air purifier operation mode. The third response mode may mean low-speed operation of the air purifier or operation off.

After the above first response mode continues for a predetermined time, when a predetermined second time (T2) is reached, the second response mode can be operated (S47). The gas management reference line (l2) can be lowered. The second response mode can mean that the ability to filter out harmful gases is increased compared to the first response mode. For example, the number of filters that filter harmful gases can be increased, or the wind speed of the air purifier can be increased. If the air purifier includes a ventilation device, the ventilation performance can also be increased. When the second response mode starts, the indoor harmful gas line (l4) can be rapidly lowered. Accordingly, a large amount of harmful gases can be removed, and the indoor space can be managed more strictly.

The above process can be performed repeatedly. Finally, it can end in the third response mode. For example, it can be performed continuously until the gas concentration becomes lower than the third reference value. For example, when the gas concentration becomes lower than the third reference value, it can return to the third response mode. For example, when the rising pattern ends while the first response mode continues, the second response mode can be ended and the third response mode can be transitioned.

The above process can be continued until the gas concentration drops below a certain level, that is, below the lowered gas management baseline. The above process can be continued for a certain period of time. In this case, the release of gas can continue for a long period of time, thereby strongly removing harmful gases.

As another example, the end of the rising pattern may not be followed during the continuation of the first response mode. In this case, when the second time (T2) is reached during the continuation of the first response mode, the second response mode may be initiated.

The second time (T2) above can define a time after a predetermined time after the first time (T1). The second time (T2) can be any time. The first time (T1) can be determined by detecting the concentration of a hazardous gas. The second time (T2) and the first time (T1) can be set based on various factors such as region, season, and humidity. For example, the interval between the first time (T1) and the second time (T2) can be short in the summer. This is because the gas concentration can quickly increase due to a high temperature environment. The second time (T2) can also be measured using the same mechanism as the first time based on the measured concentration value. For example, it can be set as the time when the concentration change per unit time reaches a second reference value that is smaller than the first reference value.

The meaning of each time domain in the above new house syndrome mode is explained in detail. Referring to Fig. 12, ① section may be a section for detecting the unit time concentration change amount. For example, it may be called a rising pattern detection section. ② section may be a section in which the gas concentration increases but the existing operation continues. In other words, it may be a section in which the rising pattern of the gas concentration increases but the gas increase is verified. For example, it may be called a rising pattern verification section. ③ section may be called the first response mode section. ④ section may be called the second response mode section.

The quantitative and qualitative effects of the above air purifier according to its usage method are explained.

Figure 17 is a drawing showing a conventional method of using an air purifier. Referring to Figure 17, conventionally, a single gas concentration is used as a management standard. Accordingly, when the gas concentration exceeds a predetermined standard, the air purifier is operated, and when it falls below the predetermined standard, the air purifier is stopped. Accordingly, according to the conventional technology, a single air purification capability and a single gas management standard are applied.

Fig. 18 is a drawing comparing the usage method of a conventional air purifier with the usage method of the air purifier of the embodiment. Referring to Fig. 18, it can be seen that the exposure amount of harmful gases to the human body is reduced by the hatched portion. For example, there may exist a first harmful gas area (101) that cannot be removed despite the need to remove harmful gases strongly, and a second harmful gas area (102) that cannot be removed because the air cannot be cleaned strongly despite the need to perform strong air cleaning because harmful gases are still generated at a high level.

The advantages of the embodiment can be understood by comparing the above-described FIGS. 17 and 18.

Hereinafter, the method of using the air purifier according to the embodiment of the present invention will be described. There are various gases that are harmful to the indoor environment. Representative examples include acetaldehyde, formaldehyde, acetic acid, toluene, and ammonia (anhydrous). The above harmful gases have different human hazards and different safety standards for each.

The above acetaldehyde is based on the TLV (Threshold Limit Value) standard: 25 ppm, STEL (ShortTerm Exposure Limit); (maximum value): A3 (confirmed as an animal carcinogen, unknown human carcinogenicity). MAK (time-weighted average exposure standard): 91 mg/㎥, 50 ppm; Peak limit classification level: I (1); Carcinogen classification level: 5; Pregnancy risk group: C; Germ cell mutation group: 5.

The above formaldehyde is based on the TLV (Threshold Limit Value) standard: 0.1 ppm, STEL (ShortTerm Exposure Limit); (SEN): A1 (confirmed as a human carcinogen). MAK (Time-Weighted Average Exposure Standard): 0.37 mg/㎥, 0.3 ppm; Peak Limit Classification Level: I(2); Carcinogen Classification Level: 4; Pregnancy Risk Group: C; Germ Cell Mutation Group: 5; Skin Sensitization (SH). EU-OEL (Occupational exposure limit values): 0.37 mg/㎥, 0.3 ppm TWA; 0.74 mg/㎥, 0.6 ppm STEL; (skin sensitizer).

The above acetic acid is EU-OEL (occupational exposure limit values): 25 mg/㎥, 10 ppm TWA; 50 mg/㎥, 20 ppm STEL; (skin sensitizer). MAK (time-weighted average exposure standard): 25 mg/㎥, 0.3 ppm; Peak limit classification level: I (2); Pregnancy risk group: C. TLV (Threshold Limit Value) standard: 10 ppm, TWA; 15 ppm STEL.

The above toluene is TLV (Threshold Limit Value, allowable concentration of hazardous chemicals) standard: 20ppm, TWA; (OTO): A4 (not classified as a human carcinogen); BEI. MAK (time-weighted average exposure standard): 190mg/㎥, 50ppm; Peak limit classification level: II(2); Dermal absorption (H): Pregnancy risk group: C. EU-OEL (occupational exposure limit values, occupational exposure limit values): 192mg/㎥, 50ppm TWA; 384mg/㎥, 100ppm STEL; (skin).

The above ammonia (anhydrous) is TLV (Threshold Limit Value, hazardous chemical substance allowable concentration) standard: 25ppm, TWA; 35ppm STEL. MAK (Time-Weighted Average Exposure Standard): 14mg/㎥, 20ppm; Peak Limit Classification Level: I(2); Pregnancy Risk Group: C, EU-OEL (occupational exposure limit values, occupational exposure limit values): 14mg/㎥, 20ppm TWA; 36mg/㎥, 50ppm STEL.

Referring to the above toxicity information, the toxic gases can be ranked in their safety order. Accordingly, the toxicity can be divided into the following order: formaldehyde > acetic aldehyde > toluene = acetic acid = ammonia. Although toluene, acetic acid, and ammonia cause an unpleasant odor, they can be evaluated as having low toxicity.

Figure 15 presents a method of using an air purifier according to an embodiment.

Referring to FIG. 15, sensing values for measuring formaldehyde (methalal), acetaldehyde (ethanal), and toluene are output using a sensing device presented in an embodiment (S51a to S51c). Here, the toluene can be replaced with acetic acid or ammonia. In addition to the toluene, a sensor for detecting other harmful gases such as acetic acid or ammonia can be further added. After acquiring the sensing values, they can be mapped to each gas (S52a to S52c), and the concentration values of each gas can be output (S53a to S53c). The concentration values can be obtained using an eigenvalue graph.

The above gases are most toxic in the order of formaldehyde (methalal), acetaldehyde (ethanal), and toluene.

It can be determined whether the concentration value of the most harmful formaldehyde exceeds the first reference value (S54a). Here, the reference value may be a value determined to be harmful. As a result of the determination, if the concentration value of formaldehyde exceeds the first reference value, the air purifier can be operated in the first mode (S55a)(S56). Here, the first mode may be an operation that lowers the current gas concentration of formaldehyde to below the target concentration. As a result of the determination, if the concentration value of formaldehyde does not exceed the first reference value, the next step can be moved to.

In the above next step, it can be determined whether the concentration value of the acetaldehyde exceeds the second reference value (S54b). As a result of the determination, if the concentration value of the acetaldehyde exceeds the second reference value, the air purifier can be operated in the second mode (S55b) (S56). Here, the second mode can be an operation that lowers the current gas concentration of acetaldehyde to below the target concentration. As a result of the determination, if the concentration value of the acetaldehyde does not exceed the second reference value, it can proceed to the next step.

In the next step, it is possible to determine whether the concentration value of the toluene exceeds the third reference value (S54c). As a result of the determination, if the concentration value of the toluene exceeds the third reference value, the air purifier can be operated in the third mode (S55c) (S56). Here, the third mode may be an operation in which the current toluene gas concentration is lowered below the target concentration. As a result of the determination, if the concentration value of the toluene does not exceed the third reference value, it may transition to the existing air purifier operation mode. The existing air purifier operation mode may be an operation mode in which a harmful gas is present but the harmfulness is low and can be ignored, or an operation mode before performing an operation corresponding to a harmful gas.

In the above usage method, each target temperature, each reference value, each mode and the above concentration value may be different from each other.

The air purifier of the embodiment has a filter that removes a specific gas and can also remove other gases. In this case, by first removing the most harmful gas, the physical damage to the user can be greatly reduced. For example, a filter that mainly removes formaldehyde but also removes acetaldehyde can be installed, and a filter that mainly removes acetaldehyde but also removes formaldehyde. In this case, when a small amount of formaldehyde is detected, the formaldehyde can be removed to reduce the harm to the body. In other words, there is an advantage in that a dangerous gas can be removed preferentially according to the degree of danger of the gas. Accordingly, the advantage of only having to partially replace the filter corresponding to a specific gas can be obtained without having to replace all the filters.

The gas sensing device of the embodiment may provide a specific sensor that detects a specific gas. That is, any one gas may be detected in correspondence with any one sensor.

The gas sensing device of the embodiment can detect a large number of gases with a small number of sensors. At least two sensors can react to at least two gases. In this case, more gases can be detected. The detected gases can be removed individually. In this case, the method of detecting gases has already been described.

The present invention can improve the economic efficiency of an air purifier.

According to the present invention, there is an advantage in that the adverse effects on the body caused by harmful gases can be reduced.

2: Filter
4: Fan Assembly
6: 1st gas sensor
7: 2nd gas sensor
101: 1st Hazardous Gas Area
102: 2nd hazardous gas area
161: 1st sensing module
162: 2nd sensing module

Claims (9)

delete delete delete delete delete Measuring the concentration of a gas;
When the concentration change per unit time of the above gas exceeds the first reference value, it is determined that the concentration of the gas is increasing, and operation is performed in the third response mode to the first response mode; and
Including driving in the second response mode when a predetermined condition is satisfied after the first response mode continues,
The above first response mode has a higher gas filtering ability than the above third response mode,
The above second response mode is a method of using an air purifier having a higher gas filtering ability than the above first response mode. In paragraph 6,
The above conditions for driving in the above second response mode are:
A method of using an air purifier, including reaching a time at any time, or reaching a time after a predetermined period of time has elapsed since the first response mode is started. In paragraph 7,
The above conditions for driving in the above second response mode are:
A method of using an air purifier, wherein the change in concentration per unit time of the above gas exceeds a first reference value. In paragraph 6,
A method of using an air purifier, wherein after driving in the second response mode, the gas management baseline (l2) stored in the memory of the air purifier becomes lower than before as a baseline for recognizing that the concentration of the gas in the air is harmful.

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